Thousands of school-issued student computers in Natick were unusable this month after administration officials encountered a bug while uninstalling an application that some students downloaded to circumvent filters that blocked Facebook, as well as gambling and pornography sites.

The Natick High School's desktop computers and laptops were restored within three days, but other computers in the district's middle and elementary schools took nearly two weeks to fix, said Dennis Roche, Natick's director of technology.

Roche said that technology officials were using a program called Casper Suite to delete an application called Tor, which some students downloaded to access websites blocked by the school's filters, when a bug accidentally deleted not only Tor, but also any running program on the computers.

"This bug deleted any running application, which included parts of the operating systems," Roche said. "This took the machines down, but also made them so they couldn?t boot back up."

Roche said that the issue also led to a complex recovery.

"Since every student could be doing something different, the bug removed different parts for everybody," he said, noting that Casper Suite company employees flew in from Minnesota to assist Natick officials. "It made the recovery process very difficult."

Roche said it was impossible to know which websites students visited while using Tor, since going around the filters also circumvented the school's ability to see which sites students used.

However, once the computers were restored and returned to students, at least 100 students tried to re-install Tor, leading the district to email parents about the problem.

School officials implored parents to keep an eye on their kid's computers, and to make sure they abide by the policies outlined in the student handbook.

"Students who choose to disregard these regulations will be subject to disciplinary consequences," the email said.

Roche said no additional funds from the district were needed to fix the problem.

"The key thing was just lost time," he said. "Students had a lot of lost time, and the technology team had a lot of lost time trying to get everything back up and running as quickly as possible."

Natick began its $2.27 million initiative to provide all high schoolers and eighth graders with a MacBook in the past few years.

The district also received national attention in September from Project RED, a national research group that studies the effects of technology in school systems, for implementing the one-to-one laptop program.